Performance evaluation and diagnosis is an important aspect of network management for all kinds of networks. In the last years, networks evolved from delivering mainly communications to delivering diversified services including content (video, games, real time streaming) and/or data. As a result the networks have experienced impressive growth in terms of infrastructure (routers and links that have been added) as well as of the number of users that they support. In this context, fault diagnosis and performance monitoring have become extremely important for network service providers. Accurate and timely knowledge of the internal status of a network (e.g., delays on individual links, congestion level) is essential for various network operations such as route selection, resource allocation, and fault diagnosis.
In the case of large scale networks, which may be substantially unregulated and highly heterogeneous, a single network operator or provider may not have control over all segments of a network that impact upon relevant performance data for that operator or provider. Certain segments of the network may therefore be unobservable, as the cooperation of network elements within those segments cannot be obtained.
Network Tomography has emerged as a promising technique enabling unobservable network performance parameters to be inferred without requiring cooperation of internal network components. Unobservable parameters are inferred solely on the basis of end-to-end (E2E) measurements conducted using edge nodes. Referring to the network 600 illustrated in FIG. 6, a series of probing paths is defined through the network, the probing paths originating and terminating with edge nodes 602-614 and traversing internal nodes 616-622. E2E measurements on data packets transmitted on the probing paths may be conducted with the cooperation of the edge nodes 602-614.
Network Tomography can work using both passive and active measurements. In the first case the system can use connections already present in the network to obtain aggregate path-level information without affecting traffic load. However, the coverage provided by such connections could not span all the paths of interest. If the available connections are not sufficient to uniquely identify all link metrics from path measurements, active probing is required. In this case, it is assumed that a set of boundary nodes is able to send probing packets to another set of edge nodes in order to measure packet attributes on the end-to-end path. However, this approach could have a potential limitation related to the possibility to freely select the paths through which probing packets are sent. Indeed, consecutive probing packets from a single source point to a specific destination could follow different paths due to routing changes or configured load balancing that can force a percentage of traffic onto an alternative link. As a result, if Network Tomography is used to infer network performance parameters the results may not be reliable because the probing packets travelling along different routes experience different delays, different jitter and/or packet loss along the route. In consequence Network Tomography findings based on a pair of source and destination nodes will not be accurate.